The aim of X-ray computed tomography is to represent the internal structure of a living body, generally for diagnostic purposes, by non-invasive examinations. Since the absorption behaviors of these structures differ only slightly, contrast medium is frequently applied to produce a high-contrast representation. The contrast medium either accumulates on specific body structures, such as carcinomas, or enriches specific body fluids, for example blood. Contrast mediums such as these generally contain elements that are distinguished by a high absorption coefficient, and therefore, provide good contrast from the surrounding tissue, with a relatively low absorption coefficient.
Conventional practice in this context is to use contrast mediums containing iodine. Contrast mediums containing gadolinium are also used because of the possibility of the patient being examined not being compatible with iodine. In this context, contrast mediums containing lanthanoid are also generally proposed. In this context reference should be made, for example, to the documents “Arterial angiography in high-kilovoltage technique with gadolinium as the contrast medium: first clinical experience”, F. Fobbe et al., Eur. Radiol. 6, 224-229 (1996), Springer-Verlag; “Evaluation of Gadobutrol in a Rabbit Model as a New Lanthanide Contrast medium for Computer Tomography”, Stephan A. Schmitz et al., Investigative Radiology, Vol. 30, No. 11, 644-649 (1995), Lippincott-Raven Publishers; “1-Molar Gadobutrol as a Contrast medium for Computed Tomography: Results from a Comparative Procine Study”, Marc Kalinowski et al., Investigative Radiology, Vol. 38, No. 4, 193-199 (2003), Lippincott Williams & Wilkins, Inc. and “Gd-DTPA: An Alternative Medium for CT” Aidan D. Quinn et al., Journal of Computer Assisted Tomography, 18(4): 634-636 (1994) Raven Press Ltd.
These documents also describe examinations which indicate the absorption of a number of specific contrast mediums in Hounsfield units. The examinations are also based on different X-ray spectra. However, these examinations provide the operator only with the knowledge that a contrast medium with a higher atomic number leads to better imaging results with the radiation that is being used. In addition, the known effect of the linear relationship between the concentration of the contrast medium and the measured absorption is described. No direct aid is provided for selection of an optimum combination of contrast medium to the X-ray spectrum for specific examination areas of a patient, and for achieving an optimum contrast-to-noise ratio.